don't delete log file upon HUP

Log.cpp

@@ -44,10 +44,12 @@ void Log::Flush ()
 		m_LogStream->flush();
 }
 
-void Log::SetLogFile (const std::string& fullFilePath)
+void Log::SetLogFile (const std::string& fullFilePath, bool truncate)
 {
 	m_FullFilePath = fullFilePath;	
-	auto logFile = std::make_shared<std::ofstream> (fullFilePath, std::ofstream::out | std::ofstream::binary | std::ofstream::trunc);
+	auto mode = std::ofstream::out | std::ofstream::binary;
+	mode |= truncate ? std::ofstream::trunc : std::ofstream::app;
+	auto logFile = std::make_shared<std::ofstream> (fullFilePath, mode);
 	if (logFile->is_open ())
 	{
 		SetLogStream (logFile);
@@ -59,7 +61,7 @@ void Log::ReopenLogFile ()
 {
 	if (m_FullFilePath.length () > 0)
 	{
-		SetLogFile (m_FullFilePath);
+		SetLogFile (m_FullFilePath, false); // don't truncate
 		LogPrint(eLogInfo, "Log: file ", m_FullFilePath,  " reopen");
 	}
 }

Log.h

@@ -38,7 +38,7 @@ class Log: public i2p::util::MsgQueue<LogMsg>
 		Log () { SetOnEmpty (std::bind (&Log::Flush, this)); };
 		~Log () {};
 
-		void SetLogFile (const std::string& fullFilePath);
+		void SetLogFile (const std::string& fullFilePath, bool truncate = true);
 		void ReopenLogFile ();
 		void SetLogLevel (const std::string& level);
 		void SetLogStream (std::shared_ptr<std::ostream> logStream);